1. Field of the Invention
The present invention relates to a tool member having a tungsten carbide (WC) based cemented carbide substrate and a diamond coating deposited thereon, in which the bonding strength between the diamond coating and the substrate is extremely high.
2. Prior Art
A conventional diamond-coated tool member of tungsten carbide based cemented carbide, which is used for tools such as a cutting insert, and end mill, a drill, and the like, is produced by grinding an outermost portion of a tungsten carbide based cemented carbide substrate, subsequently subjecting the substrate to chemical etching with dilute nitric acid, sulfuric acid, and the like to remove cobalt (Co) existing in the outermost portion of the substrate, and forming a diamond coating having an average layer thickness of 0.5 .mu.m-20 .mu.m on the substrate by a known vapor deposition method. The tungsten carbide based cemented carbide substrate has generally the following composition in terms of % by weight, excluding unavoidable impurities:
cobalt as a binder phase forming component: 1% to 25%; PA1 optionally, as a dispersed phase forming component, at least one material selected from the group consisting of carbides of metals selected from Groups IV.sub.A, V.sub.A, and VI.sub.A of the Periodic Table and their solid solutions: 0.5% to 30%; and PA1 tungsten carbide as the dispersed phase forming component comprising the reminder of the composition. PA1 sintering a green compact to produce a tungsten carbide based cemented carbide substrate; PA1 grinding the tungsten carbide based cemented carbide substrate; PA1 subsequently heat-treating the tungsten carbide based cemented carbide substrate at a temperature between 1000.degree. C. and 1600.degree. C. in a vacuum or in a non-oxdizing atmosphere; and PA1 subsequently forming a diamond coating on the substrate by a vapor-deposition method.
In the conventional diamond-coated tool member of tungsten carbide based cemented carbide mentioned above, however, the bonding strength between the diamond coating and the substrate is low. Therefore, when the tools formed of the tool members are used for interrupted cutting of Al-Si alloy or the like or for heavy-duty cutting such as high feed cutting and deep cutting, the diamond coating is susceptible to separation from the substrate, and the tool life is relatively short.